Abstract: A method of sludge concentration comprises forming a froth in the foaming zone by mixing a foaming agent, air and water, mixing the sludge feed with said froth and a polymeric flocculant in a mixing zone, and introducing the resulting mixture of sludge and flocculant into a flotation zone for separating the mixture into a concentrated sludge and water is disclosed.

Abstract: An activated-sludge process for wastewater treatment comprising the steps of:(1) feeding raw wastewater to an aeration tank containing activated sludge;(2) supplying air into the aeration tank to produce aerobic and anaerobic areas in said tank;(3) separating sludge from the mixed liquor coming out of the aeration tank and concentrating at least part of the separated sludge or said mixed liquor in a concentrator to thereby produce concentrated sludge and separated water; and(4) feeding the concentrated sludge into the aeration tank and maintaining the MLSS concentration in said tank at a value between 7,000 to 15,000 mg/liter, thereby removing the organic matter and nitrogen components from the wastewater within said aeration tank.

Abstract: In the treatment of wastewater by the activated sludge process, mixed liquor in the aeration tank or settled sludge is drawn from the system and concentrated. The concentrated sludge is returned to the aeration tank either immediately or after being mixed with separated water and settled sludge to thereby reduce the SVI of the mixed liquor in the aeration tank.

Abstract: A method and an apparatus of incinerating dewatered sludge without using an auxiliary fuel comprising pelletizing the partially dewatered sludge having a water content of 70 to 75%, drying the pellets with a heat source obtained by burning gases formed by dry-distillation and gasification, using part of the resulting dry-distilled gas in said drying step, dry-distilling the pellets by the sensible heat of a gas formed by gasification, gasifying the dry-distillation residues with air, water vapor and the remainder of said dry-distilled gas.

Abstract: A method for treating excess sludge, which comprises the steps of mixing an inlet stream of waste water with activated sludge, aerating the resulting mixture, separating the effluent water from the activated sludge to be recycled to the mixing step, passing the resulting excess sludge to a conversion stage, treating therein the cells of microorganisms composing suspended solids in said excess sludge to convert them to an organic liquid by a physical and/or physico-chemical means, passing the resulting organic liquid to a digesting stage in which activated sludge takes the organic liquid as a nutrient, aerobically digesting therein the organic liquid and discharging an effluent from the digesting stage.